Generally, electron emission devices are classified into those using hot cathodes as the electron emission source, and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a surface conduction emitter (SCE) type.
The MIM-type and the MIS-type electron emission devices have electron emission regions with a metal/insulator/metal (MIM) structure and a metal/insulator/semiconductor (MIS) structure, respectively. When voltages are applied to the two metals or the metal and the semiconductor on either side of the insulator, electrons migrate from the high electric potential metal or semiconductor to the low electric potential metal where the electrons are accumulated and emitted.
The SCE-type electron emission device comprises a thin conductive film formed between first and second electrodes arranged facing each other on a substrate. High resistance electron emission regions or micro-crack electron emission regions are positioned on the thin conductive film. When voltages are applied to the first and second electrodes and an electric current is applied to the surface of the conductive film, electrons are emitted from the electron emission regions.
The FEA-type electron emission device uses electron emission regions made from materials having low work functions or high aspect ratios. When exposed to an electric field in a vacuum atmosphere, electrons are easily emitted from these electron emission regions. Electron emission regions having sharp front tip structures have been used. These electron emission regions mainly comprise molybdenum (Mo), silicon (Si), or a carbonaceous material such as carbon nanotube, graphite, or diamond-like carbon.
The above-identified electron emission devices commonly comprise first and second substrates facing each other. Electron emission regions are positioned on the first substrate, and an anode electrode and phosphor layers are positioned on the second substrate such that the electrons emitted from the electron emission regions collide with the phosphor layers, thereby emitting light. The anode electrode receives positive (+) voltages ranging from several hundred to several thousand volts and directs the electrons emitted from the electron emission regions toward the phosphor layers.
A focusing or grid electrode is sometimes positioned between the first and second substrates. The focusing or grid electrode increases the focusing capacity of the electron beams emitted from the electron emission regions. As the thickness of the focusing electrode increases, its electron beam focusing capacity and its ability to intercept the anode electric field before the electric field reaches the electron emission regions are enhanced.
Currently available focusing electrode film formation techniques, like sputtering, cannot form focusing electrodes with thicknesses of 1 μm or more. Therefore, metallic mesh-shaped grid electrodes having a plurality of beam guide holes in a predetermined pattern have been used instead of focusing electrodes. However, it is difficult to form small beam guide holes on the metal plate, and to correctly locate the grid electrode between the first and second substrates.